This invention relates to an adjustment drive for adjusting devices of a motor vehicle seat.
From DE 10 2004 040 602 A1 an actuating drive for an electric seat adjuster of a motor vehicle seat is known, which comprises a drive motor and a two-stage, self-locking reduction gear which converts a fast rotary drive movement of the drive motor into a reduced, slow rotary movement of a driven gear. The reduction gear has a housing with a lower part flange-mounted to the drive motor, an intermediate plate with a radial groove and a cover part which is screwed to the lower part by means of screws by interposition of the intermediate plate. The first, self-locking reduction stage of the reduction gear is formed by a worm-gear drive which contains a drive worm connected with the axis of rotation of the drive motor, which engages into a spur toothing of a spur gear. With the spur gear an eccentric of an eccentric gear forming the second reduction stage is connected, which includes a wobble gear, the driven gear cooperating with the wobble gear via a toothing, and a guide means for the wobble gear, which is non-rotatably held by means of the guide means and is enabled to carry out a wobbling movement on a circular path. The guide means comprises a guide arm molded to the wobble gear, which is shiftably and non-rotatably held in the radial groove of the intermediate plate in a radial direction relative to the circular path.
In the plurality of gear elements arranged axially one behind the other of the first and second reduction stage of the reduction gear and in the radial guidance of the wobble gear there is a risk that in particular with a high load the toothings can get out of engagement, which not only means an inoperability of the actuating drive, but above all a considerable risk of injury for the motor vehicle occupants in the case of a crash.
As an alternative to a radial guidance of the wobble gear, it is known from DE 41 27 051 A1 in a reduction gear formed as wobble or planetary gear system with an internally toothed ring gear connected with a driven shaft and with a planet gear whose external toothing partly is in engagement with the internal toothing of the ring gear, to use a cross-head slide for the horizontal and vertical guidance of the planet gear, which includes a vertically oriented oblong hole which at its ends merges into vertical slots, into which trunnions engage which are arranged diametrically to each other on the end face of the wobble gear. In horizontal legs of the cross-head slide two horizontal oblong holes aligned with each other are provided, into which trunnions firmly connected with a housing cover are immersed.
An alternative eccentric gear for the transmission fitting of a vehicle seat is known from EP 1 647 438 B1, in which on an eccentric connected with a carrier a planet gear with two concentric external toothings with different tip-circle diameters is arranged, of which the first external toothing meshes with the internal toothing of a frame-side ring gear and the second external toothing meshes with the internal toothing of an output-side ring gear. Since the number of teeth of the planet gear differs from that of the ring gears by at least one tooth and the respective outside diameter of the external toothing of the planet gear is smaller than the inside diameter of the frame-side or output-side ring gear by at least one tooth height, the planet gear performs gearing-up of the rotary movement, which is transmitted from the carrier via the eccentric to the planet gear.